1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_ 6 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_ 7 8 #include <cstring> 9 #include <functional> 10 #include <type_traits> 11 #include <vector> 12 13 #include "base/optional.h" 14 #include "mojo/public/cpp/bindings/lib/template_util.h" 15 16 namespace mojo { 17 namespace internal { 18 19 template <typename T> 20 size_t HashCombine(size_t seed, const T& value) { 21 // Based on proposal in: 22 // http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf 23 return seed ^ (std::hash<T>()(value) + (seed << 6) + (seed >> 2)); 24 } 25 26 template <typename T> 27 struct HasHashMethod { 28 template <typename U> 29 static char Test(decltype(&U::Hash)); 30 template <typename U> 31 static int Test(...); 32 static const bool value = sizeof(Test<T>(0)) == sizeof(char); 33 34 private: 35 EnsureTypeIsComplete<T> check_t_; 36 }; 37 38 template <typename T, bool has_hash_method = HasHashMethod<T>::value> 39 struct HashTraits; 40 41 template <typename T> 42 size_t Hash(size_t seed, const T& value); 43 44 template <typename T> 45 struct HashTraits<T, true> { 46 static size_t Hash(size_t seed, const T& value) { return value.Hash(seed); } 47 }; 48 49 template <typename T> 50 struct HashTraits<T, false> { 51 static size_t Hash(size_t seed, const T& value) { 52 return HashCombine(seed, value); 53 } 54 }; 55 56 template <typename T> 57 struct HashTraits<std::vector<T>, false> { 58 static size_t Hash(size_t seed, const std::vector<T>& value) { 59 for (const auto& element : value) { 60 seed = HashCombine(seed, element); 61 } 62 return seed; 63 } 64 }; 65 66 template <typename T> 67 struct HashTraits<base::Optional<std::vector<T>>, false> { 68 static size_t Hash(size_t seed, const base::Optional<std::vector<T>>& value) { 69 if (!value) 70 return HashCombine(seed, 0); 71 72 return Hash(seed, *value); 73 } 74 }; 75 76 template <typename T> 77 size_t Hash(size_t seed, const T& value) { 78 return HashTraits<T>::Hash(seed, value); 79 } 80 81 } // namespace internal 82 } // namespace mojo 83 84 #endif // MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_ 85
